The interactions of bromocriptine and lergotrile with dopamine and with alpha receptors were investigated. Both drugs have mixed agonist-antagonist activities with respect to dopamine receptors. Lergotrile has a higher affinity for the agonist site than bromocriptine. Both drugs displace the binding of the alpha-adrenergic antagonist WB-4101. Bromocriptine displaces more effectively than lergotrile the binding WB-4101 from the cerebral cortex membranes. Lergotrile mesylate, an ergot alkaloid derivative and putative dopamine agonist, was effective in the majority of patients with Parkinson's disease who were showing signs of disease progression despite treatment with levodopa combined with a peripheral decarboxylase inhibitor (carbidopa). Among 20 patients completing a six-month trail, there was a significant (p less than .01) reduction in rigidity, tremor, bradykinesia, gait disturbance, and total score when lergotrile was added to levodopa plus carbidopa. Mean daily dose of lergotrile mesylate was 52 mg, and the mean daily dose of levodopa was reduced by 15%. Abnormal involuntary movements were decreased on addition of lergotrile and reduction in levodopa while mental changes and orthostatic hypotension were increased.